Systems or devices that require thermal conditioning, i.e., heating or cooling, more often than not require at least a portion thereof to fall within a specific thermal profile in order to function optimally or properly. With regard to conduction based heating systems (i.e., those characterized by a transfer of thermal energy between adjacent bodies or parts thereof owing to the presence of a temperature gradient), thermo-electric heaters are commonly used to produce and input required heat. Such heaters convert electrical energy into heat energy and provide a motive thermal force for conductive heat transfer.
Thermo-electric heaters are generally either applied to a non-working surface area on, or embedded within, the bulk of a mass, generally called a heat-sink, on which the working surface resides. In the context of a thermal conditioning system comprised of a thermo-electric heater and heat sink, temperature sensing and monitoring is advantageously undertaken to measure and indicate system temperatures, advantageously as a function of time, in relation to the heat-sink in furtherance of providing input or feedback to a control system.
Meaningful conductive heat transfer is premised upon substantial, uniform, homogeneous physical contact between, for and among the thermo-electric heater and the heat-sink. In instances when physical contact is lost, conductive heat transfer is lost. In instances where only a portion of the original contact area is lost the system may still be able to maintain the temperature of the heat-sink in the vicinity of the heat sensing element, however, the local or localized temperature at the point where the heater and the heat-sink have separated is likely to be drastically altered (i.e., greatly departed from that indicated by the heat sensing element). Moreover, while the heat-sink temperature at the separation local will thusly be lower than what is generally intended, the temperature of the thermo-electric heater at that local will be higher. This can have at least two detrimental effects.
On the heat-sink, the temperature may drop below the select, necessary temperature required for a chemical or physical process to occur or proceed, especially time critical processes. For example, process gases of a semiconductor processing chamber may not fully react with a top surface of a silicon wafer under process, or the surface temperature on the leading edge of an aircraft wing may not reach the temperature necessary to shed built up ice.
Within the thermo-electric heater, at the local where the heater and the heat-sink have separated, the heating element continues to generate the same quantity of heat as when the now locally disassociated elements were operatively united/associated, however, the generated heat has a much smaller means of conducting out, hence the thermo-electric heater element temperature, and its associated, surrounding electrical insulation, rapidly increase in temperature. Depending upon the magnitude of the temperature rise and/or its profile (i.e., temporal rate of change), the thermo-electric heater element electrical insulation can experience a change in its electrical insulating properties, outgas volatile compounds into the environment, or even combust. With regard to the heating element of the thermo-electric heater, degradation in the form or fracturing, melting, etc. often occurs, with the imparted system stress potentially resulting in the ignition of local/localized gases and/or materials adjacent to or in the vicinity of the thermo-electric heater element.
In light of the foregoing, an elegantly simple and reliable heater failure detection approach remains warranted. More particularly, a solution or solutions to heater failure detection over considerable temperature and power densities is believed advantageous and desirable. More particularly still, there remains outstanding a need for a readily monitorable fail safe heater assembly characterized by a thermo-electric heater, a resistive sensor, and an optionally integral heat sink.